X-ray part



X-RAY PART Filed DGO. l, 1951 Patented Apr. 3, 1934 Westinghouse LampCompany,

Pennsylvania a corporation of Application December 1, 1931, Serial No.578,244

Claims.

This invention relates to electrical discharge devices and moreparticularly to devices of this character employed. for the productionof X-rays and commonly termed X-ray tubes. In its more g specific aspectthe invention is directed to the provision of electrical dischargedevices and especially IST-ray tubes which during construction oroperation will not fail because ci envelope puncture caused byelectrical stresses.

An X-ray tube design which has found application in a number ofdifferent fields generally comprises an elongated envelope having aplurality of oppositely disposed electrodes therein. '111e envelope iscomposed of glass or the like and consists of a cylindrical body portionhaving a generally hemispherical upper end and a lower end with areentrant tube extending upwardly therewithin and spaced from theinterior thereof. The free end of the reentrant tube is sealed to atubular metallic and generally copper sleeve carrying the anode and alsoserving as a means of electrical connection by means of an anodeextension connected thereto. Within said envelope and fused thereto is aSecond reentrant tube hav- I ing a major portion spaced from the sidesthereof and extending upwardly in the envelope, spaced from andsurrounding the anode.

Tubes ci this character require a great deal of care and time inpractical production. The anode, cathode, X-ray screen and a portion ofthe metallic cap as weil as the interior of the envelope and thereentrant tubes are carefully cleaned before the tube assemblage. Thesealing operation of the metallic tubular sleeve to the upper portion ioi' the reentrant tube generally results in the outer surface thereof,or what is the surface thereof located within the completed tube,becoming covered with a layer or coating of metallic oxides or othercompounds.

A portion of said area may be readily freed from said coating by eitherchemical or mechanical means, but it is not generally feasible to removethe coating in close proximity of the metallic-glass seal without eitherpuncturing the '51 metallic sleeve or breaking the seal which must bekept air tight. In the course of practical operation or seasoning oftubes of this character it sometimes has been found that the tubepunctured at that or in proximity to the place of ring 50 fusion orseal.

l"The basis reason for this puncturing I believe is due primarily tolthe oxides, other compounds or impurities on the metallic sleeve. Oneexplanation at which I have arrived is that when a high voltage, withinthe operating voltages and normal (Cl. Z-35) surge voltages, are appliedto the terminals oi the tube, the anode as well as the sleeve is heatedand particles of matter which I believe to be positive ions are expelledfrom the coating and deposited on the inner wall or the envelope. Thesepar-4 ticles of matter build up a charge on the inner wall o1" the tubeat the areas of deposition and thereby increase the liability ofpuncture at these areas, which puncture does sometimes occur.

In order to obviate this diiiiculty and to thus minimize the liabilityof envelope puncturing clue to electrical stresses, I have developed thefollowing invention which in its briefest aspect comprises shielding theenvelope and especially the seal of the second reentrant tube from thosepor- 7 tions oi its internal structure which are not clean surfaced, andparticularly from the coating at the seal of the reentrant tube andmetallic sleeve. For this purpose I may employ a simple expedient in theform of a shielding skirt. 7

This shield is spaced from, surrounds the metallic sleeve-glass seal andserves as a barrier to prevent most if not all of the impurities such asthe metallic compounds or other impurities at or y Y adjacent the sealfrom traveling to and deposit- 80 ing on the envelope and especially ator adjacent the place of union ci the envelope and second reentranttube.

An object of my invention is to provide an electrical discharge tubewhich will withstand comparatively high voltages without envelopepuncture.

Another object of my invention is to provide an X-ray tube having asimple expedient incorporated therein which serves to minimize thedanger of its envelope puncture.

Another object of my invention is tor provide an X-ray tube capable ofoperating at the practical voltages encountered in tube operationwithout puncturing of the envelope.

Other objects and advantages of my invention will become apparent fromthe following specification and appended drawing wherein,

Fig. 1 represents a longitudinal cross sectional View with some of theparts in elevation of an X-ray tube having a part broken away andembodying my invention.

Fig. 2 is a cross sectional view of Fig. 1 along the line II--II in thedirection of the arrows.

According to my invention the X-ray tube 105,

and has a major portion of its wall spaced from and surrounded by thebody portion. To this reentrant tube is hermetically sealed a tubularmetallic and preferably copper sleeve or support coupling 14.

This sleeve has a thin annular portion to which the upper end of thereentrant tube 13 is hermetically sealed by following the common processgenerally employed for this purpose.

This sleeve or support coupling 14 has a threaded recess in which isscrewed a metallic and preferably a copper rod 15 which functions as ananode extension and serves as a heat and electrical conducting element.The outer portion of said sleeve or support coupling 14 is also threadedand is secured thereat to an anode 16. This anode 16 may be of anysuitable metallic material and preferably copper, extending upwardlywithin the envelope and along the longitudinal axis thereof. The upperor free end (not shown) of the anode has a target of suitable material,such as tungsten or the like embedded therein and serving as an X-rayemitting material upon bombardment thereof by the electrons from asuitable filamentary cathode (not shown).

Disposed around and having its interior wall spaced from the free end ofthe anode 16 is an X-ray screen 18 consisting of nickel-iron. This X-rayscreen houses the cathode and a focusing cup (both not shown). Thecathode is electrically connected to a plurality of conductors 19 and 20which are hermetically sealed to the envelope 10 and electricallysecured to contact caps 21 and 22 respectively. Surrounding thismetallic screen and functioning to provide a screen supporting and shockabsorbing means are a plurality of resilient plates 23 which bearagainst the outer surface of said screen and the interior of theenvelope.

Located within the envelope and extending upwardly therewithin is asecond reentrant tube 24 surrounding and spaced from the tubular sleeve14 and the anode 16.

This reentrant tube is of a material length and has its lower edgefusedly united with the envelope at about the lowermost quarter lengthof the envelope and as shown slightly below the seal of the firstreentrant tube 13 and the tubular sleeve 14.

Spaced around said anode 16 and bearing thereagainst are a plurality ofresilient supporting and shock absorbing plates 25. The plates 25function as frictional bearing resilient elements bearing against theouter surface of the anode 16 and the inner surface of the reentranttube 24 to provide a rugged structure.

In the course of production of electrical discharge devices andespecially X-ray tubes of this character it is advisable to surfaceclean as much as possible all of the internal parts of the tube. Inpractice, any impurities, such as dirt, oxide films or the like areremoved from the cathode leads, the cathode, the anode, the screen andthe resilient plates before assembly thereof. The tubular sleeve orsupport 14 is freed as nearly as possible from any of the oxides, othercompounds or impurities thereon which may have been produced during thesealing of the reentrant tube 13 with the tubular sleeve 14. Asheretofore stated, it is possible to so treat the major portion of saidsleeve 14 by either a mechanical or chemical process to provide it witha clean surface, but it is not feasible to clean either chemically ormechanically the seal per se or that area immediately adjacent the seal,the latter of which generally is of a darker hue than the cleanedportion and indicated by the reference character A.

With a construction of this character I have observed that when avoltage is applied between the anode and the cathode that sometimes theenvelope punctures at or in proximity of the area of ring fusion of thesecond reentrant tube 24 and the envelope 10.

In order to avoid this difficulty and in further accordance with mypresent invention, there is provided a shielding means 30 around thetubular sleeve 14 to prevent any impurities in the form of unchargedparticles or positive ions from going directly to the envelope in thevicinity of the fusion ring of the reentrant tube 24 and the envelope10. This shielding means 30 may be composed of a dielectric andpreferably a conducting material such as copper, and may be in the formof a cup having a suitably sized opening in its base adapted toaccommodate the upper threaded portion of the tubular sleeve 14. Thiscup shaped copper shielding means 30 may be expeditiously manufacturedat a comparatively low cost by a simple drawing operation. Thereafterthis cup may be readily cleaned by a mechanical and preferably achemical process to remove all impurities such as oxides, othercompounds or other impurities from the surface thereof.

The shielding means 30 is appropriately dimensioned so that uponassembly thereof with the other elements of the tube, it rests on theshoulder portion of the tubular sleeve and extends therearound anddownwardly at least as far as and preferably materially below the sealof the tubular sleeve 14 and the reentrant tube 13.

As is apparent from the drawing this shielding means 30 may be readilyapplied by simply projecting the upper threaded end of the sleeve 14through the opening in the base of the shielding means. The anode 16 isthereafter screwed on to said end to provide an even bearing between thelower end of the anode 16 and the upper surface of the bottom of thecup, and the lower surface of the bottom of the cup and the shoulder ofthe tubular sleeve.

Besides improving the electrical characteristics of the tube, thisshielding means 30 imparts to the tube as a whole a finer and cleanerappearance because it shields from view the seal as well as the tubularsleeve having a portion thereof which appears to have been overlooked inthe cleaning operation.

What is claimed is:

1. An electrical discharge device comprising a gas tight dielectricenvelope, a plurality of electrodes therein, said envelope having areentrant tube in the lower portion thereof, an electrode supportingmember forming a hermetic seal with the upper end of the reentrant tubeand having impurities on the surface thereof adjacent said seal, one ofsaid electrodes being electrically connected to said supporting memberand a shielding means depending from said supporting member, spaced fromand surrounding a portion of said supporting member and said seal.

2. An electrical discharge device comprising a gas tight dielectricenvelope, a plurality of electrodes therein, said envelope having areentrant tube in the lower portion thereof and a second reentrant tubefusion ring sealed to the interior of said envelope, an electrodesupporting member forming a hermetic seal with the upper end of said rstmentioned reentrant tube and having impurities on the surface thereofadjacent said seal, one of said electrodes being electrically connectedto said supporting member and shielding means spaced from andsurrounding a portion of said supporting member and said seal, saidshielding means also supported by said supporting member, said secondreentrant tube also supporting said electrode connected to saidsupporting member.

3. An X-ray tube comprising a dielectric gas tight envelope, asupporting member, a plurality of electrodes therein, one of saidelectrodes connected to the supporting member forming a hermetic sealwith a portion of the envelope and having impurities on the surfacethereof adjacent said seal, and shielding means within the envelopelocated between said supporting member and the envelope, said shieldingmeans having a portion thereof located between said electrode and saidsupporting member.

4. An X-ray tube comprising a gas tight dielectric envelope, asupporting member, a plurality of electrodes therein, said envelopehaving a reentrant tube in the lower portion thereof and a secondreentrant tube fusion ring sealed to the interior of said envelope, saidsupporting member forming a hermetic seal with said first mentionedreentrant tube and having impurities on the surface thereof adjacentsaid seal, one of said electrodes connected to said supporting memberand means spaced from and shielding said seal and supporting member fromthe envelope, said means depending from said supporting member, saidsecond reentrant tube also supporting said electrode connected to saidsupporting member.

5. An X-ray tube comprising a gas tight dielectric envelope, a pluralityof electrodes therein, said envelope having a reentrant tube in thelower portion thereof, a supporting member hermetically sealed to saidfirst mentioned reentrant tube and having impurities thereon adjacentsaid seal, a second reentrant tube fusion ring sealed to the interior ofsaid envelope and extending upwardly

